Strut angle conundrum

[Guest]

Re: Strut angle conundrum

some info

Part 1 says; Maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.

AC 43.13-1b mentions straightening on page 4-73 of chapter 4,
a.Location of Splices. Steel-brace struts may be spliced at any point along the length of the strut provided the splice does not overlap part of an end fitting. The jury-strut attachment is not considered an end fitting; therefore, a splice may be made at this point. The repair procedure and workmanship minimize distortion due to welding and the necessity for subsequent straightening operations.

Just showing that straightening is a recognized procedure.

[woodmw]

Re: Strut angle conundrum

Airframes Alaska states on their webpage that the heat used in the powder coating procedure can destroy the properties of the oil inside the strut and may distort the strut shape. When heating to bend, can you shunt enough heat from the rest of the strut to prevent the degradation of the oils or distorting the strut?

[PA1195]

Re: Strut angle conundrum

They are presented as "lifetime sealed struts" so I wonder why worry about compromising any oil entombed in the strut, especially in a limited area that was heat treated to reform? Linseed oil or Stits' Tubeseal are frequently applied to airframes and yet welders routinely repair them. Distortion? Who knows but I'd want the temp specs of their exclusive powder coating process before judging their method versus others (reported as typically ~200*C/400F).

Powder coating was the rage for Alaskan airframes but I've heard rebuilders that now have shied away after observing the effects of years of field service for some examples. Not my expertise however.

Powder coating adds substantially to the overall cost and profit of the product. I chose to have my AA struts painted over a durable primer to level the cost and allow for field repairs.

As far as heat forming I'd ask the strut manufacturer if that compromises their lifetime durability.

Gary

[astjp2]

Re: Strut angle conundrum

Corrosion under the powder coat which you cant see easily and you cant see the cracks until it has a hard fracture. I would like to see everything yellow zinc plated and no paint...but I am not sure that is approved, but it would be much lighter. Tim

[Guest]

Re: Strut angle conundrum

Corrosion under the powder coat which you cant see easily and you cant see the cracks until it has a hard fracture. I would like to see everything yellow zinc plated and no paint...but I am not sure that is approved, but it would be much lighter. Tim

Yes Tim is correct, I have experienced that many times.

I happened on parts of my Kubota tractor/loader/backhoe, lawn mowing equipment and 3 point hitch equipment.

Suddenly the nice painted finish peels of like a hard boiled eggshell (actually easier than an eggshell) and underneath is a very corroded metal surface.

I would never powder coat an airplane part although I suspect many will disagree.

I like primer then yellow enamel over steel parts.

Dave R.

[Guest]

Re: Strut angle conundrum

Airframes Alaska states on their webpage that the heat used in the powder coating procedure can destroy the properties of the oil inside the strut and may distort the strut shape. When heating to bend, can you shunt enough heat from the rest of the strut to prevent the degradation of the oils or distorting the strut?

I think so. Of course the 2-3 inches that you heated at the end will have the oil burnt off but that being the very top of the strut makes it less of an issue.

Dave R

[Guest]

Re: Strut angle conundrum

They are presented as "lifetime sealed struts" so I wonder why worry about compromising any oil entombed in the strut, especially in a limited area that was heat treated to reform? Linseed oil or Stits' Tubeseal are frequently applied to airframes and yet welders routinely repair them. Distortion? Who knows but I'd want the temp specs of their exclusive powder coating process before judging their method versus others (reported as typically ~200*C/400F).

Powder coating was the rage for Alaskan airframes but I've heard rebuilders that now have shied away after observing the effects of years of field service for some examples. Not my expertise however.

Powder coating adds substantially to the overall cost and profit of the product. I chose to have my AA struts painted over a durable primer to level the cost and allow for field repairs.

As far as heat forming I'd ask the strut manufacturer if that compromises their lifetime durability.

Gary

One of the worst experiences that I ever had was repairing tubes on a fuselage that the prior fixer put par-al-ketone (as best as I could identifiy it, it was par-al-ketone) in as the rust inhibitor.

Never had issues with linseed oil, I bet that's what Stits Tube is also as it smells like it. I have some Piper struts that have a very thing coating on the inside looks like clear undercoat. That is probably hard to work on.

Dave R

[Robert Lees]

Re: Strut angle conundrum

Airframes Alaska states on their webpage that the heat used in the powder coating procedure can destroy the properties of the oil inside the strut and may distort the strut shape. When heating to bend, can you shunt enough heat from the rest of the strut to prevent the degradation of the oils or distorting the strut?

I would not entertain any powder-coating on any structural steel part of any aircraft. The flexibility of the coating can hide a multitude of sins hiding under the thick surface.
So NO to powder-coating on struts, engine mounts etc.

As an aside, the ten sets of struts I got from Alaska Airframes were delivered in " primer" for corrosion protection during shipment. 5 years later, I had to strip mine down to bare metal and paint them properly because I don't believe AA applied the primer to a properly cleaned surface (they were not powder-coated back then).

Use an etch-prime on the bare and CLEAN steel, then epoxy two-pack primer, then top coat of your choice. It's saves a lot of grief, and it makes sense.


Just my opinion.
Rob

[astjp2]

Re: Strut angle conundrum

so far its only the Alaska airframes ones with the angle issues, I have not heard of any wag, factory or univair problems...so what does that tell you?

[Hank Jarrett]

Re: Strut angle conundrum

My set that didn't fit were from Wag. They were great to work with and did everything possible to help fix any problems. I don't think it is an AA problem. Haven't bought from AA yet but haven't heard bad things either.
ANY company can put out a part with a problem. What matters is how they deal with problems..Never had a problem with how Wag handled ANY problem. If you wanted a company that had LOTS of parts problems you would be thinking Taylorcraft under Harry I. Lucky for all T owners he is no longer an issue.


Hank

[Guest]

Re: Strut angle conundrum

so far its only the Alaska airframes ones with the angle issues, I have not heard of any wag, factory or univair problems...so what does that tell you?

Hi Tim,

I wondered about that also.

What perplexes me is that IF it was problem with the fabrication of the strut then an airplane with an 8 degree strut from AA could have that strut removed and replaced by a 2 degree strut from another source (like Wag or Uni or an old used one).

I am not aware of any examples of that.

If it turns out not to be true then there is a difference in airplanes (for what ever reasons).

Dave R

[Hank Jarrett]

Re: Strut angle conundrum

Dave, that IS what happened to mine. As I said, they were from WAG and I had to ship them back where they did "something" that got the angle to fit. Mine were some of the very early struts from them so at that time they probably didn't even know that there were different strut angles.

My suspicion is that the factory strut tooling was "damaged" in some way and a correction was made to the wing tooling to correct for it. This kind of thing happens when you move the factory tooling. I can tell you for sure that it is common for shop floor tooling to be "adjusted" on the floor and many times the engineers never are told. We had it happen several times on the Grumman A-6 and it gets the plane in front of the mechanic relief quickly to just "adjust" the tooling, but causes this kind of problems down the line. It was a common reason that interchangeable parts weren't.

I can tell you for sure that when I get ready to do the assembly of the 45 I have it will be completely assembled WITHOUT COVERING so that these kinds of "adjustments" can be made in the buck naked state. With planes as old as ours some parts are just going to have to be custom fit. Not all interchangeable parts are.

Hank

[Mark Bowden]

Re: Strut angle conundrum

It is very possible that the powder coat cure temperature could relieve and distort a weld assembly.

On corrosion under powder coat, you still have to conversion coat prime before you powder coat just like liquid top coat. Primer is the protection.

That's why internal parts never get top coated, it's not needed and it adds cost and weight. Industry use of bare clad aluminum parts used the 1000 series layer as the conversion coating (worked just ok and not well in coastal areas!). But primer is better over bare alloys.

Top coats, liquid paint or powder, are there to look pretty and offer protection to the conversion primer, both have their merits and good applications. Key to remember in topcoat finish selections is that it just doesn't matter what you pick at all if you don't:
1. properly clean for the alloy of the part to remove ALL contaminants, including ALL corrosion
2. get all the cleaning media, solid or chemical fully removed
3. properly apply a conversion coating primer in strict adherence to the instructions and in a timely manner so corrosion doesn't restart

Conversion primers will "self-heal" through a crack or scratch, however, "self-heal" is a bad term that is commonly used. The primer doesn't close back over the scratch. It still protects by the fact that primer edge is still more easily sacrificed than the exposed metal but within limits of the width and depth of the scratch. Repair the scratch right away.

Primers are tested in this fashion. Multiple plates, about 4 x 6" are prepped & primed, then scratched in an X to a consistent depth & width. Plates are placed in a salt fog chamber per an ASTM test procedure and exposed for constant periods of time. After each time step, one of the plates is sectioned and corrosion is measured. You can also do outdoor tests to add the natural effects of UV exposure and the elements to qualify your primer selection.

There are a few good applications for powder on an aircraft part. Lot of powder coatings are porous, bad for protection; some are "functional" and less porous for exposure to the elements or chemicals or stone chips, etc...